whats algorithm of Exim message ID [closed] - email-headers

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i want know a message id in Exim how to generate.
for example : 1YSWPk-0000oX-0N
also Message id in headers
Message-ID: <aa1e23e76be8b95bc21718a4c4e000fc#example.com>
and can decode these?
and any relationship with these and other email headers?

Answer 1

Exim's specification part 3.4 says that
The first six characters of the message id are the time at which the
message started to be received, to a granularity of one second. That
is, this field contains the number of seconds since the start of the
epoch (the normal Unix way of representing the date and time of day).
After the first hyphen, the next six characters are the id of the
process that received the message.
There are two different possibilities for the final two characters:
If localhost_number is not set, this value is the fractional part of
the time of reception, normally in units of 1/2000 of a second, but
for systems that must use base 36 instead of base 62 (because of
case-insensitive file systems), the units are 1/1000 of a second.
If localhost_number is set, it is multiplied by 200 (100) and added to
the fractional part of the time, which in this case is in units of
1/200 (1/100) of a second.
Here are the headers of message sent from my exim to the gmail.com.
Lines 19-27 are generated by my MTA/exim while all lines above are generated by gmail servers.
1 Delivered-To: kondybas#gmail.com
2 Received: by 10.27.143.12 with SMTP id r12csp943315wld;
3 Tue, 3 Mar 2015 12:49:41 -0800 (PST)
4 X-Received: by 10.180.126.69 with SMTP id mw5mr50725522wib.12.1425415780590;
5 Tue, 03 Mar 2015 12:49:40 -0800 (PST)
6 Return-Path: <root#domain.tld>
7 Received: from domain.tld (relay.domain.tld. [11.22.33.44])
8 by mx.google.com with ESMTPS id y2si3224153wjy.199.2015.03.03.12.49.40
9 for <kondybas#gmail.com>
10 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
11 Tue, 03 Mar 2015 12:49:40 -0800 (PST)
12 Received-SPF: pass (google.com: domain of root#domain.tld designates 11.22.33.44 as permitted sender) client-ip=11.22.33.44;
13 Authentication-Results: mx.google.com;
14 spf=pass (google.com: domain of root#domain.tld designates 11.22.33.44 as permitted sender) smtp.mail=root#domain.tld;
15 dkim=pass header.i=#domain.tld
16 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=domain.tld; s=s;
17 h=Date:From:Message-Id:Subject:To; bh=g3zLYH4xKxcPrHOD18z9YfpQcnk/GaJedfustWU5uGs=;
18 b=p7JbGnGFvxdvL0UESIprvXTXq1GcQTeWZOTy3nrTOynwqHz9JEKQu+nqNU6iZtC7LxmPBbOFXjy3Qbg9vH3BLdaqivk/duFSUoYenFQgQd/iaoZ8sBP3lWXx/Uz6yIy7zH2ySOZO5M/NKfG2QqZsJ8PCChJ01mCSe6bqHfcywbrAi2ZJWws3Kt3lAGIxHkdOjhcCsljrirGCCeYc8WI8PQ==;
19 Received: from root by domain.tld with local (Exim 4.85 (FreeBSD))
20 (envelope-from <root#domain.tld>)
21 id 1YStl5-00010z-JV
22 for kondybas#gmail.com; Tue, 03 Mar 2015 22:49:39 +0200
23 To: kondybas#gmail.com
24 Subject: test
25 Message-Id: <E1YStl5-00010z-JV#domain.tld>
26 From: Charlie Root <root#domain.tld>
27 Date: Tue, 03 Mar 2015 22:49:39 +0200